2nd engine.lot of miles..oil gAUGE needle bounces back/forth. on 1997 Dodge Dakota

idles gauge to zero,check engine lt comes on. 1. how to install a oil gauge? 2. how to change the oil pump?screen could be clogged?truck had belonged to in-laws,kept poor maintenance! even after it warms up,needle bounces....i was thinking oil pump change out.truck stays parked till resolved...thanks for any info.

Asked by for the 1997 Dodge Dakota